Github user andreweduffy commented on a diff in the pull request:

    https://github.com/apache/spark/pull/15835#discussion_r87500313
  
    --- Diff: 
sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/parquet/ParquetFileFormat.scala
 ---
    @@ -272,6 +275,83 @@ class ParquetFileFormat
         true
       }
     
    +  override def getSplits(fileIndex: FileIndex,
    +                         fileStatus: FileStatus,
    +                         filters: Seq[Filter],
    +                         schema: StructType,
    +                         hadoopConf: Configuration): Seq[FileSplit] = {
    +    if (filters.isEmpty) {
    +      // Return immediately to save FileSystem overhead
    +      super.getSplits(fileIndex, fileStatus, filters, schema, hadoopConf)
    +    } else {
    +      val filePath = fileStatus.getPath
    +      val rootOption: Option[Path] = fileIndex.rootPaths
    +        .find(root => filePath.toString.startsWith(root.toString))
    +      val metadataOption = rootOption.flatMap(getMetadataForPath(filePath, 
_, hadoopConf))
    +      // If the metadata exists, filter the splits.
    +      // Otherwise, fall back to the default implementation.
    +      metadataOption
    +        .map(filterToSplits(fileStatus, _, rootOption.get, filters, 
schema, hadoopConf))
    +        .getOrElse(super.getSplits(fileIndex, fileStatus, filters, schema, 
hadoopConf))
    +    }
    +  }
    +
    +  private def filterToSplits(fileStatus: FileStatus,
    +                             metadata: ParquetMetadata,
    +                             metadataRoot: Path,
    +                             filters: Seq[Filter],
    +                             schema: StructType,
    +                             hadoopConf: Configuration): Seq[FileSplit] = {
    +    val metadataBlocks = metadata.getBlocks
    +    val parquetSchema = metadata.getFileMetaData.getSchema
    +    val filter = FilterCompat.get(filters
    +          .flatMap(ParquetFilters.createFilter(schema, _))
    +          .reduce(FilterApi.and))
    +    val filteredMetadata =
    +      RowGroupFilter.filterRowGroups(filter, metadataBlocks, 
parquetSchema).asScala
    +    filteredMetadata.flatMap(bmd => {
    +      val bmdPath = new Path(metadataRoot, bmd.getPath)
    +      val fsPath = fileStatus.getPath
    +      if (bmdPath == fsPath) {
    +        Some(new FileSplit(bmdPath, bmd.getStartingPos, 
bmd.getTotalByteSize, Array.empty))
    +      } else {
    +        None
    +      }
    +    })
    +  }
    +
    +  private def getMetadataForPath(filePath: Path,
    --- End diff --
    
    I think this should be cacheable, as the lifetime of a `FileFormat` is tied 
to a particular `HadoopFsRelation`, which again is tied to a `Dataset`. 
Something may have changed about the API but from a quick look through the 
relevant classes I don't see anything to refute this. I don't see any written 
guarantees in the FileFormat API that concrete impls need to be stateless, but 
neither did I find any reference to caching/state in other implementations. 
Still I think it should be safe to cache on the ParquetFileFormat for this use 
case.


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